Contact lenses, in particular soft contact lenses for single use, are nowadays produced in great volumes in highly automated manufacturing processes and facilities. These contact lenses can be manufactured using reusable male and female mold halves which are typically made of glass. When mated to form the mold these mold halves define a hollow mold cavity between the lens forming surfaces of the male and female mold halves, and this lens cavity corresponds to the shape of the contact lens to be formed. Prior to mating the male and female mold halves to close the mold a lens forming material which may be a polymer or pre-polymer solution is dosed into the female mold half. Suitable lens forming materials include polymers or pre-polymers based on polyvinyl alcohols (PVA), on silicone hydrogels (SiHy) or on polyethylene glycols (PEG), or other suitable lens forming materials as are known in the art. After closing the mold, the lens forming material contained in the mold cavity is cured through polymerization and/or cross-linking to form the contact lens.
During manufacturing of such contact lenses it may occur, that air bubbles get entrapped in the lens forming material. For example, such entrapment of air bubbles may occur in a boundary region of the lens forming material and the lens forming surface of the female mold half as the lens forming material is dispensed into the female mold half. Such entrapment may in particular occur when a lens forming material having a high viscosity is used. In case such highly viscous lens forming material is dispensed into the female mold half at the center of the female mold half, the surface of the female mold half may not get properly wetted and air bubbles may get entrapped which may not escape during further wetting of the lens forming surface. To avoid this, the material can be dispensed into the female mold half off-center. Another possibility of air bubble entrapment is at the boundary surface of the lens forming material and the male mold half as the male mold half is mated with the female mold half to close the mold. This may in particular occur with a lens forming material having a low viscosity (but may also occur with a highly viscous lens forming material). It is believed that the formation of air bubbles may be the result of a non-uniform and/or non-symmetric wetting of the respective mold half by the lens forming material. For example, as the male mold half is advanced towards the lens forming material contained in the female mold half, in case the first contact of the lens forming surface of the male mold half does not occur at a predefined single point this may result in a non-homogeneous wetting of the lens forming surface of the male mold half and to the entrapment of air bubbles. The entrapped air bubbles may lead to a poor lens quality, thus resulting in rejection of the contact lens.